This invention relates generally to sump pumps and more particularly to a circuit which monitors and controls the charging of a rechargeable battery used to drive a sump pump.
In the operation of a conventional sump pump, the pump is equipped with a float switch which turns the pump motor on only when the water level in the sump rises high enough to close the float switch. Rechargeable batteries are often used to supply the electrical power for operating the pump motor.
One of the problems with battery powered sump pumps is that the charge/discharge condition of the battery is not controlled in a way to maximize its useful life. Typically, time delay circuits are used to charge the battery, and the battery is not always fully charged during the charge cycle. Other units operate virtually indefinitely in the charging mode and thus overcharge the battery and reduce its operating life by reason of the overcharged battery condition. Conversely, the pump motor can run so long that it pulls the battery charge down below a level where it can be recharged successfully. Again, the life of the battery suffers accordingly. Some sump pump systems have an audible or visual alarm that is activated to provide an indication of an unduly low battery charge. The indicator drains even more current and causes the battery to discharge even more quickly to a condition where it cannot be recharged.
It is thus evident that a need exists for a sump pump in which the battery is continuously monitored so that its charge/discharge cycles can be controlled properly to maximize the operating life of the battery. It is the principal goal of the present invention to meet that need.
More specifically, it is an important object of the invention to provide, in a battery powered sump pump, a monitoring circuit which monitors the condition of the battery at all times and a charging circuit that acts automatically to charge the battery when needed, without overcharging or allowing the battery charge to drop so low that recharging is impossible. In accordance with the invention, the battery voltage is monitored by comparators which control the state of two flip flop circuits. One of the flip flops controls a logic gate that allows the pump motor to operate and the other flip flop controls a charging circuit for the battery.
The circuitry is arranged to automatically turn the charging circuit on when the battery voltage drops to a low level of about 10.5 volts and to automatically turn the charging circuit off when the battery voltage reaches a high level of about 13.6 volts. Thus, the battery is never allowed to discharge enough to damage it or prevent it from being recharged, and overcharging of the battery is also precluded. If the battery is above an intermediate level about (12.5 volts), the pump is controlled wholly by the float switch. In the range of 10.5-12.5 volts, the pump can be turned on by the float switch only if the charging circuit has charged the battery sufficiently to energize a "ready" indicator at about 12.5 volts. Consequently, the battery is allowed to discharge only to 10.5 volts where lockout of the pump occurs, and it is then charged to a relatively high level of at least 12.5 volts before the pump can be cycled on again (discontinuing the lockout function) thus preventing the battery from discharging unduly while providing only a relatively short period of additional pump operation. Unless the float switch closed during the charging cycle, the battery is fully charged (to about 13.6 volts).
The circuit of the present invention lends itself to incorporation in an integrated circuit having suitable interfaces with the mechanical float switch, the pump motor, a transformer which supplies charging current and a piezoelectric alarm which audibly indicates when the pump is running. LED indicators are provided to indicated the state of operation of the system, and membrane switches permit reset and test functions to be effected.